Kiln for ceramic products

ABSTRACT

A kiln of relatively simple design is provided for firing ceramic ware. The kiln is of the shuttle type consisting generally of a rectangular refractory enclosure with a movable floor which may consist of cars supporting the ware. Burners of the excess air type are provided in the upper part of the kiln to induce downward flow of hot combustion gases through the ware. The hot gas exhausts into a system of ducts in the side walls of the kiln and a major part of the hot gas is returned to the burners for turbulent mixing with the products of combustion and recirculation through the ware.

United States Patent 1191 2/l940- Breeler 432/137 X Fay Dec. 17, 1974 [54] KILN FOR CERAMIC PRODUCTS 3,219,328 11/1965 Miller 432/137 [75] Inventor: Gordon C. Fay, P1ttsburgh, Pa. Primary Examinr johni J. Camby I v [73] Assignee: Hendryx Engineers Incorporated, Attorney, Agent, or FirmBr0wn, Murray, Flick &v

Pittsburgh, Pa. Peckham v [22] F1led: Nov. 9 1973 ABSTRACT [21] Appl' 414,444 A kiln of relatively simple design is provided for firing Ceramic ware. The kiln is of the shuttle type consisting 52 US. Cl 432/137, 432/146, 432/149, generally of a rectangular refractory enclosure, With a Y 432/153 movable floor which may consist of cars supporting 51 1m. c1. F27b 9/00 the Wate- Burners 0f the excess r yp are Provided [58] Field of Search 432/137, 146, 149, 153 in the pp P of the kiln to induce downward flow of hot combustion gases through the ware. The hot gas 56] References Cited exhausts into a system of ducts in the side walls of the I UNITEDSTAI-ES ATENTS kiln and a major part of the hot gas is returned to the burners for turbulent mixing with the products of i'gg'g'gg 2x23; 2153;: 432/137 combustion and recirculation ,throughthe ware.

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1 KILN FOR CERAMIC PRODUCTS BACKGROUND OF THE INVENTION The present invention relates to kilns for firing ceramic products such as brick, sewer pipe, refractories and the like.

In the manufacture of such ceramic products it is necessary to fire the molded clay ware in a kiln at a high temperature for a substantial period of time. One type of kiln sometimes used for this purpose consists generally of a rectan'gularrefractory enclosure provided with burners for heating the ware which is stacked on cars for movement into and out of the kiln. Kilns of this type, often referred to as shuttle kilns, have the great advantage of flexibility in use but have had the disadvantages of high capital cost and high fuel costs as compared to some other types of kilns. The major reason for the high fuel costs is that these kilns have usually been of updraft design in which the products of combustion only pass over or through the ware once. The burners are placed at the bottom-or lower part of the kiln, and the hot combustion gases flow up-' ward through the ware and are exhausted at the top of the kiln. Thus the hot gases make only one pass over the ware and any heat not transferred to the ware during this one pass is lost up the stack. This results in relatively low efficiency in transmitting heat from the prod ucts of combustion to the ware, and in utilization of the fuel. A large quantity of fuel is therefore required to heat the ware to the necessary temperature, resulting in high fuel costs. Furthermore, it is difficult to maintain uniform temperature at each of the burners, and the gases must be forced or guided in some way to overcome the tendency for the hottest, and therefore lightest, gases to channel in an upward flow, and to cause the gases to flow more or less uniformly through the stacked ware to produce a sufficiently uniform temperature throughout the ware.

Attempts have been made to'build kilns of this general type forv downdraft operation in order to obtain better fuel economy and more uniform heat distribution. Such attempts, however, have resulted in quite complicated and expensive constructions, requiring underground flues beneath the kiln and hightemperature exhaust fans capable of handling the hot gas exhausted from the kiln. In many cases, complicated and expen sive burner controls have also been required to control the burners in the manner necessary to provide uniform heat distribution.

SUMMARY OF THE INVENTION In accordance with the present invention, a kiln generally of the shuttle type is provided for firing ceramic products which is relatively simple in design and which can be operated with low fuel costs as compared to prior kiln designs. These results are obtained by providgenerally rectangular refractory enclosure with a movable floor which may take the form of a plurality of cars for supporting the ware and moving it into and out of the kiln. Burners are provided in the upper part of the kiln, above the ware. The hot, gaseous products of combustion flow downward through the ware, and the burners can be suppplied with excess combustion air to provide a large volume of high velocity heated gas. The gas flowing downward through the ware is exhausted through the floor of the kiln and laterally below the ware into a duct system in the side walls which includes 7 BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood fromthe following detailed description, taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevation of a kiln embodying the invention;

FIG. 2 is a transverse sectional view substantially on I the line IIII of FIG. 1;

FIG. 3 is a transverse sectional view substantially on the line III.III of FIG. 1;

FIG. 4 is a horizontal sectional view substantially on the line IV-IV of FIGS. 1 and 3;

FIG. 5 is a fragmentary side view of a car; and FIG. 6 is a fragmentary transverse sectional view of a kiln showing a somewhat modified arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT An illustrative embodiment of the invention is shown in the drawings. As there shown, the kiln 10 may comprise a generally rectangular enclosure having side walls 12 and a roof 14. The walls 12 may be of usual construction, being built up of refractory brick with a blanket of kaolin wool, .or similar material, and an outer steel jacket 18. The walls are supported in a structural steel framework 20 of usual type. The roof 14 is a sprung arch type of roof of insulating refractory brick with an outer covering 22 of refractory cement or other insulation. The kiln may be closed at both ends by doors 23, or one end may be permanently closed. The doors may be of any suitable or usual construction which is capable of being tightly sealed when the kiln is in operation.

The bottom of the kiln 10 is closed by movable floor members which preferably take the form of cars 24 movable in and out of the kiln on tracks 26. The walls 12 and tracks 26' are suitably supported on transverse structural members 27 with the tracks positioned in the proper vertical location relative to the walls. Each of the cars 24 has a base portion 28 which is substantially impervious to gas and which, as shown in FIG. 5, may be built up of refractory blocks 30 supported on a structural steel framework 31 and packed with refractory insulation to provide an impervious base. The base portion 28 carries wheels 32 which run on the tracks 26. The car 24 has a flat upper surface 33 which forms the floor of the kiln and on which the ware 34 to be fired is stacked. The ware may be any desired ceramic product and may include brick, sewer pipe, refractories, and other ceramic and structural clay products. As illustrated in the drawings, the ware 34 consists of brick which is stacked in the manner shown to permit free flow of hot kiln gases through the ware so as to uniformly heat all parts of the stack. Other types of ware may be similarly stacked to permit flow of gas therethrough.

The gas flowing downward through the ware 34 flows through the floor surface 33 of the cars and is exhausted laterally through suitable passages in the cars. In the illustrative construction shown in FIGS. 2, 4 and 5, each car 24 has a plurality of rows of pier blocks 36 disposed on the base 28 so as to form ducts or passages 37 between the rows of blocks, the blocks being somewhat spaced apart in each row to equalize gas pressures. The upper portion of the car 24 which forms the floor of the kiln is made up of rectangular refractory blocks 38 supported on the pier blocks 36 and laid so as to form a continuous level floor surface 33 on which the ware can be stacked. The blocks 38 have holes 40 therethrough to permit free flow of gas downward through the floor surface 33 and into the passages 37 through which the gas can flow laterally .to be exhausted at the sides of the car. Each side of the car has a sealing-flange 42 extending downward in position to pass behind a flange 44 secured in the adjacent side wall 12 of the kiln. This permits the formation of a conventional sandseal 46 on each side of each car to substantially seal the floor of the kiln below the level of the passages 37 through which the hot gases exhaust from v the cars. Any conventional type of seal may be pro vided as indicateddiagrammatically at 48, to seal the ends of the cars together so that the bottom of the kiln is effectively sealed against escape ofgas. The cars may, of course, be permanently or semi-permanently sealed together at their ends for movement of the complete set of cars into and out of the kiln as a unitary assembly, thus forming, in effect, a complete movable floor for the kiln.

In some instances, for greater capacity or flexibility, a two-track or multiple track arrangement may be utilized as shown in FlG. 6. As there shown, two tracks 26 extend through the kiln and two sets of cars 24 are provided running on the tracks 26. A wall 50 of refractory brick extends down the center of the kiln between the two tracks and preferably to a height about at the level of the floor surfaces 33 or slightly above. The wall 50 has seal members 52 which extend under the sealing flanges 42 on the cars to permit the formation of sandseals between the cars and the wall 50. In other respects, the kiln is identical to that described above except that the gases exhaust primarily to one side of the cars instead of both sides.

I-lot' gas forheating the ware is supplied by a plurality walls 12 at a level above the ware 34. Each of the burners comprises va refractory burner block 54 having a suitable passageway therethrough and provided with a fitting 56 for connection to a gas or other fuel supply and a fitting 58 fol-connection to an air supply. The

blocks 54 are mounted in the wall 12 and a venturi block 60 is provided in front of each burner block 54 and spaced a short distance therefrom. The blocks 60 are also refractory blocks'cemented into the wall 12 in alignment with the blocks 54 and having relatively large venturi passages as shown. The burners 54 are excess air burners, as will be more fully discussed'hereinafter, and a common air supply is provided for all the burners. As shown in FIG. 2, the air supply is provided by a blower 62 which has sufficient capacity to supply all the burners. The air from the blower 62 passes through a duct 64 which extends upward and across the top of the kiln and which supplies headers 66 extending along each side of the kiln. Each of the burners 54 is connected by means of its fitting 58'to one of the headers 66.

The burners 54 may burn gas, or fuel oil, and produce hot gaseous products of combustion which are di rected into the space under the roof at the top of the kiln under sufficient pressure to induce a downward flow of gas through the ware 34. In accordance with the present invention, a substantial part of the gas thus flowing downward through the ware is redirected to the burners and recirculated through the kiln. For this purpose, a horizontal flue or duct 68 is provided in each of the side walls 12 and extends horizontally the full length of each side wall. The ducts 68 are'positioned near the bottom of the walls extending below the levelof the top surface 33 of the cars24, and a series of ports 70 is provided in the side walls communicating with the ducts 68. The ports-70 are located opposite the passages 37 to receive the gases flowing laterally through the cars 24, so that the gas exhausted from the cars flows through the ports 70 into the ducts 68. A plurality of vertical ducts 72 is built into the side walls 12, a duct being provided for each burner extending up from the horizontal duct 68 and communicating with the space between the. burner 54 and its associated venturi block 60. A vent stack 74 is also provided at each end of each of the horizontal flues 68 for exhaust of gas. The circulation of gas in the kiln is shown by the arrows in FIGS. 1 and 2. The heated gas in the top of the kiln flows downward through the stacked ware 34, through the floor surface 33 of the cars 24, and is exhausted laterally through the passages 37 and the ports 70 into the horizontal flues 68. Gas flows in both directions through the flues 68, and a large volume of hot gas flows upward through the vertical ducts-72 and is aspirated by the venturi blocks 60 to mix with the combustion gases from the burners 54. Excess gas is exhausted from the flues through the vertical stacks 74 at the four corners of the kiln. The recirculated gas flow ing through the ducts 72 mixes with the combustion gases as it is aspirated through the venturi blocks into so that a large volume of hot combustion gases at a controlled flame temperature is discharged at high velocity from the burners through the venturi blocks and into the space under the roof. This gas mixes in the venturi block with the ,hot recirculated gas from the ducts 72 which is strongly aspirated by the high velocity burner gases and which may have a volume several times the volume of the products of combustion coming from the burners. Thus, a large volume" of heated gas is discharged at high velocity into the top of the kiln for circulation downward through the ware. The blower 62 is preferably operated to maintain a pressure of the order of a few hundredths of an inch of water in the upper part of the kiln to induce the downward flow of gas, with essentially a neutral pressure or draft at the level of the floor 33. The gases are exhausted through the cars into the flues 68 which supply the gases for recirculation through the ducts 72 and which exhaust to the atmosphere through the stacks 74 at each end. These stacks can be quite short since they are not required to produce any substantial amount of draft.

This operation of the new kiln design has several important advantages. The downdraft operation of the kiln positively insures uniform heating of the ware and is obtained in a relatively simple manner without requiring underground flues or high temperature fans capable of handling the hot exhaust gas. The use of high velocity excess air burners as described results in thorough mixing of the combustion gases from the burners and the recirculated gas, and provides a large volume of gas for uniform downdraft flow through the ware. The recirculation of a large volume of hot gas greatly increases the total volume of gas available for flow through the ware. This sharply increases the rate at which heat can be transferred to the ware and particularly to the bottom of the stacked ware. The time required to heat the ware uniformly from top to bottom is accordingly reduced, with corresponding fuel economy. The combination of excess air burners with recirculation of hot gas, in addition to the advantages mentioned above, makes it possible to circulate a large volume of gas at high velocity and at a relatively low temperature. The large volume of gas is important since the gas is the medium by which heat is transferred from the burners to the ware, and the more medium is utilized the more heat can be transferred. Thus, by circulating a large volume of gas, even at relatively low temperature, the ware is heated more rapidly than would be possible without the recirculation of kiln gas, and the total time required and the amount of fuel consumed are reduced. The recirculation also makes it possible to operate at higher flame temperatures and with less excess air than would be required if the products of combustion from the burners went directly through the ware without being mixed with recirculated hot gas. The recirculated gas somewhat cools the products of combustion from the burners down to a temperature appropriate for the ware on which the gases impinge. This means that less excess air has to be heated and eventually lost up the stack, so that less fuel is required.

' form and rapid heating of the ware in the kiln so that fuel consumption is kept to a minimum and the time required for heating is minimized which also tends to reduce the fuel consumption. Thus, improved operation and simplicity of design are obtained together with improved fuel economy as compared to conventional kiln designs.

I claim as my invention:

1. A kiln for firing ceramic ware comprising a generally rectangular enclosure having movable floor means for supporting the ware and closing the bottom of the enclosure, said floor means being movable into and out of the kiln and having openings for flow of gas therethrough, means for inducing a recirculating flow of hot gases downward through the ware including a plurality of burners in the upper part of the kiln, means for sup-' 2. A kiln as defined in claim 1 and including means for supplying excess air to said burners to provide a large volume of high velocity combustion gases.

3. A kiln as defined in claim 2 in which the'bumers are supported in the sides of the kiln above the ware.

4. A kiln as defined in claim 3 and including a block having a venturi passage therethrough disposed in front of each burner, said recirculated gas being directed to the spaces between the burners and said blocks.

5. A kiln as defined in claim 4 and including duct means in the sides of the kiln for receiving said gas exhausted through the floor means and directing at least part of the gas to said spaces.

6. A kiln as defined in claim 1 in which said floor means comprises a plurality of cars having passages for flow of gas therethrough, and means for effecting substantially gastight seals between the cars and between each car and the adjacent sides of the kiln below said passages.

7. A kiln for firing ceramic ware comprising an enclosing structure having side walls and a roof, movable floor means for supporting the ware within the enclosing structure, a plurality of burners disposed in said walls above the ware, means for supplying excess air to said burners for combustion, said floor means permitting combustion gases to flow downward through the ware and including means for exhausting the gases laterally below the ware, a horizontal flue extending longitudinally in each side wall, ports in each wall in position to receive gases exhausted through the floor means and communicating with said horizontal flues, and vertical ducts in the side walls extending from the horizontal flues to each of said burners for recirculation of said ases.

8. A kiln as defined in claim 7 and including an exhaust stack at each end of each of said horizontal flues.

9. A kiln as defined in claim 7 and including venturi means associated with each burner for effectively mixing said recirculated gases with combustion gases from the burner.

10. A kiln as defined in claim 7 and including a block having a venturi passage therethrough disposed in front of each burner, said vertical ducts communicating with the spaces between the burners and said blocks.

11. A kiln as defined in claim 7 in which said floor providing a floor surface for the kiln, said floor surface having openings for flow of combustion gases therethrough, and means for supporting said upper portion on the base portion, said supporting means providing passages for flow of said gases toward the sides of the car. s a 

1. A kiln for firing ceramic ware comprising a generally rectangular enclosure having movable floor means for supporting the ware and closing the bottom of the enclosure, said floor means being movable into and out of the kiln and having openings for flow of gas therethrough, means for inducing a recirculating flow of hot gases downward through the ware including a plurality of burners in the upper part of the kiln, means for supplying at least sufficient air to said burners for complete combustion to induce high velocity flow of combustion gases, said burners constituting the sole source of heat for the kiln, and means for exhausting gas flowing downward through said openings in the floor means and directing at least a part of said gas back to the burners for mixing with the combustion gases from the burners for recirculation downward through the ware.
 2. A kiln as defined in claim 1 and including means for supplying excess air to said burners to provide a large volume of high velocity combustion gases.
 3. A kiln as defined in claim 2 in which the burners are supported in the sides of the kiln above the ware.
 4. A kiln as defined in claim 3 and including a block having a venturi passage therethrough disposed in front of each burner, said recirculated gas being directed to the spaces between the burners and said blocks.
 5. A kiln as defined in claim 4 and including duct means in the sides of the kiln for receiving said gas exhausted through the floor means and directing at least part of the gas to said spaces.
 6. A kiln as defined in claim 1 in which said floor means comprises a plurality of cars having passages for flow of gas therethrough, and means for effecting substantially gastight seals between the cars and between each car and the adjacent sides of the kiln below said passages.
 7. A kiln for firing ceramic ware comprising an enclosing structure having side walls and a roof, movable floor means for Supporting the ware within the enclosing structure, a plurality of burners disposed in said walls above the ware, means for supplying excess air to said burners for combustion, said floor means permitting combustion gases to flow downward through the ware and including means for exhausting the gases laterally below the ware, a horizontal flue extending longitudinally in each side wall, ports in each wall in position to receive gases exhausted through the floor means and communicating with said horizontal flues, and vertical ducts in the side walls extending from the horizontal flues to each of said burners for recirculation of said gases.
 8. A kiln as defined in claim 7 and including an exhaust stack at each end of each of said horizontal flues.
 9. A kiln as defined in claim 7 and including venturi means associated with each burner for effectively mixing said recirculated gases with combustion gases from the burner.
 10. A kiln as defined in claim 7 and including a block having a venturi passage therethrough disposed in front of each burner, said vertical ducts communicating with the spaces between the burners and said blocks.
 11. A kiln as defined in claim 7 in which said floor means comprises a plurality of cars movable into and out of the kiln, and means for making substantially gas-tight seals between cars and between each car and the adjacent walls below said ports.
 12. A kiln as defined in claim 11 in which each of said cars has an impervious base portion, an upper portion providing a floor surface for the kiln, said floor surface having openings for flow of combustion gases therethrough, and means for supporting said upper portion on the base portion, said supporting means providing passages for flow of said gases toward the sides of the car. 